1. Field
Embodiments relate to a method and an apparatus for quantum cryptographic communication, and more particularly, to a technique for distributing secure keys regardless of a measurement device.
[Description about National Research and Development Support]
This study was supported by the Information Communication Technology R&D program of Ministry of Science, ICT and Future Planning, Republic of Korea (Project No. 2014-044-014-002) under the superintendence of Korea Institute of Science and Technology.
2. Description of the Related Art
Recently, as communication security becomes an issue due to large-scale personal information leakage, the demand on a safe cryptographic system is increasing. Generally, cryptographic systems do not use physical phenomena but use mathematical conundrums which lower the probability of hacking. Therefore, the probability of hacking a cryptographic system and analyzing encrypted information from outside still exists.
Meanwhile, quantum cryptography is a cryptographic system which has been developed based on uncertainty of quantum mechanics in which a single photon exhibiting a quantum effect cannot be reproduced. Communication subjects share the same secure key safely by using quantum to encrypt or decrypt information by using the key. Theoretically, if hacking is attempted from the outside, the characteristics of photon change, and thus the original secure key or information cannot be obtained from the outside, thereby ensuring a hacking-free cryptographic system.
In fact, however, hacking may be possible due to defects or imperfection of a measurement device used for the quantum cryptographic system. Therefore, studies about a measurement-device-independent quantum key distribution system (MDI QKD) capable of distributing a secure key regardless of a measurement device have been carried on.
FIG. 1 is a block diagram schematically showing a measurement-device-independent quantum cryptography system. Referring to FIG. 1, a first quantum code sending device (Alice) 110 and a second quantum code sending device (Bob) 120 respectively include a light source 101 and a light source 102, and convert an optical pulse generated from the light sources 101, 102 into an optical signal having information and transmit the optical signal to a quantum cryptographic communication apparatus (Charlie) 100 through a quantum channel 104. After that, the quantum entanglement measuring unit 103 measures a relation between a plurality of received optical signals by using a quantum entanglement base and distributes common information to both quantum code sending devices 110, 120 to ensure a secure key distribution system regardless of a measurement device.
However, in an existing measurement-device-independent quantum cryptography system, the light sources 101, 102 of a plurality of quantum code sending devices 110, 120 should be perfectly identical not to be distinguished, and a device (or, an active control) for measuring a difference of attributes of optical signals generated from the light sources 101, 102 and feeding back the attributes to be identical is required. However, this feedback device may not be practically commercialized due to difficult implementation and great costs.